The bottlenose dolphin (Tursiops truncatus) is found throughout the year in the waters near Tsujishima island, Amakusa, Kyushu, Japan. Recently number of watching boats have increased in the waters. It is now suspected that their approaching to the dolphins may some bad effects on this wild animal. The objective of this study is to obtain ecological information associated with conservation and management of the Tsujishima bottlenose dolphin population.Theodolite tracking was carried out on the hill of Tsujishima island. Number of the dolphin schools was commonly one. The dolphin school moved longitudinally in parallel with coast lines. Its occurrence concentrated in the waters off 1-2 km from the shore and of depth less than 20m. A regular diurnal pattern in its movement was recognized, that is, it moves in the eastern part of the waters in the morning, stays in front of the island near noon, and moves westward near sunset.Photo-identification was attempted using notches of the dorsal fin. A total of 192 individuals was identified. Some of them resighted in every season and some of them resighted continuously in 9 seasons. In consideration that the school was found on all the days of theodolite survey and that no information on common findings was available in adjacent waters, the dolphins occurring in the Tsujishima island waters constitute a resident population.Population size was estimated by a capturerecapture method. Preliminary estimates by month ranged 201-323 individuals (cv : 11.4-22.9%)